Bearing isolator seals are commonly used in a variety of rotating shaft applications when it is necessary to exclude contaminants or process fluid from reaching internal mechanisms such as shaft support bearings, or from leaking out of a housing that is penetrated by the rotating shaft.
For example, bearing isolator seals are used in bearing housings for pumps, motors, gearboxes and other pieces of rotating equipment. The main purpose of a bearing isolator seal is to prevent the ingress of process fluid or other contaminants into the bearing, which can lead to premature failure of the lubrication and bearings. In fact, penetration by contaminants is the most common reason for rotating equipment failure.
For many applications, lip seals and simple labyrinths have proven inadequate for preventing ingress of contamination into bearings. In many cases, the use of bearing isolator seals can extend rotating equipment lifespans by a factor of 2 to 5, as compared to the typical equipment lifespans when standard lip seals or simple labyrinths are used.
Some bearing isolator designs include a static “shut off” feature that seals the air gap between the rotor and the stator of the bearing isolator seal when the equipment is not running. Examples of such designs are presented in FIGS. 1A through 2, where the design of FIGS. 1A-1C includes a shut off O-ring, and the design of FIG. 2 utilizes inclines in different orientations to perform the static sealing function. FIGS. 1B and 1C are enlarged cross sectional views of the “VBX Ring” of FIG. 1A that includes the shut off O-ring. Typically, the shut off feature includes an O-ring 100 that rotates with the rotor 102 and surrounds an extension of the stator 104. When the rotor 102 is rotating, as is illustrated in FIG. 1B, the O-ring 100 is expanded away from the stator 104 by centrifugal force and, hopefully, does not interfere with rotation of the rotor 102 relative to the stator 104. But when the rotor 102 is static, as is shown in FIG. 1C, the O-ring 100 is allowed to contract and seal against the stator extension 104, so as to seal the gap between the rotor 102 and the stator 104.
Unfortunately, in this approach it can be difficult to provide a desired degree of static shut off without also avoiding any residual contact or “interference” between the O-ring and the stator when the rotor is rotating. The result can be a compromise between wear and resistance due to residual O-ring interference when the mechanism is in operation, versus the degree of seal protection provided when the mechanism is idle.
Also, axial misalignment is a major concern for shut off mechanisms of this type, and must be accounted for in the design of a static shut off feature. Typically, there can be a tendency for the rotor to move axially away from the stator during operation, causing axial “misalignment” between the rotor and the stator, and to return to a closer static or “neutral” position when the system is idle. However, most shut off designs, such as the one shown in FIGS. 1B and 1C, are intolerant of axial misalignment between the rotor and the stator, and many require that the axial misalignment be limited to only 0.007 inch (0.18 mm) Total Indicator Reading (“TIR”) or less. As a result, many applications that require a greater degree of tolerance to axial misalignment are not suitable for use with a simple shut off mechanism such as the one shown in FIGS. 1B and 1C, and require use of other, more complicated and expensive designs.
What is needed, therefore, is a cost-effective bearing isolator seal having a static shut off feature that is tolerant of axial misalignment between the rotor and stator, and which provides an improved static seal between the rotor and the stator while minimizing wear and resistance when the rotor is rotating and axially misaligned relative to the stator.